Experimental and Theoretical Investigations of Electron Capture and Transfer Dissociation of Protonated and Alkaliated Model Peptoids

摘要

In general, peptoids show very similar fragmentation behavior under ECD and ETD tandem MS conditions when compared to peptides. In addition to common C- and Z-type fragment ions and extensive loss of neutrals originating from side chains, Y- and B-type fragment ions were observed, as well as with C-1-, C+1&2-, and Z+1&2-type fragment ions. ECD spectra of [Peptoid+2H]~(2+) ions are more informative than ETD spectra. In ETD spectra abundant ETnoD ions were observed. ECD spectra of [Peptoid+2H]~(2+) and [Peptoid+H+Na]~(2+) ions show quite different fragmentation behavior, which may be due to different peptoid ion conformations. In [Peptoid+H+Na]~(2+) ions after ECD or ETD the proton has been neutralized and the sodium ions is the sole charge carrier. Addition of two protons does not disrupt the engineered helical backbone conformation of peptoids. A simple ion-ion repulsion model based on the single and double protonation of n-alkyl diamines allowed a quick estimation of the possible second protonation sites and their corresponding proton affinities. IRMPD spectra of the same peptoid ions showed other and more diverse fragmentation behavior.